The present invention relates to a scroll compressor, more particularly relates to a seal means suitable for providing a backpressure chamber supporting a thrust load of a scroll compressor.
As described in Japanese Unexamined Patent Publication (Kokai) No. 2-176178, when driving a movable scroll to compress a fluid in a scroll compressor, a thrust load pressing the movable scroll to the fixed housing side is generated due to the compression reaction force. To support this thrust load, a ring-shaped thrust load support member comprised of a member comprised basically of for example cobalt or nickel and including a secondary ingredient such as molybdenum, chrome, silicon, or carbon or a wear resistant material comprised of carbon fiber bound by an epoxy resin is used between a back surface of an end plate of the movable scroll and the surface on the housing side facing this. With this configuration, however, heat of friction due to the sliding action is generated between the front surface of the thrust load support member and the surface of the opposing member and wear progresses, so in the related art, the measure has been devised of providing a groove in the ring-shaped thrust load support member to supply cooling water to absorb the heat of friction.
To suppress the heat of friction or wear in the thrust load support member generated in this way, as described in the invention previously proposed by the inventors and disclosed in Japanese Unexamined Patent Publication (Kokai) No. 9-310687, there is known a scroll compressor formed with a backpressure chamber as a recessed space in a back surface of an end plate of a movable scroll and guiding a compressed fluid from a discharge side to this backpressure chamber to cause the generation of a backpressure and thereby bias the movable scroll in an axial direction and reduce the large contact load acting between the back surface of the flat surface of the movable scroll on the housing side generated by the compression reaction force.
When working the related art described above, if the fluid to be compressed is one with a low working pressure as with the chlorofluorocarbons generally used as refrigerants in refrigeration cycles, the thrust load generated due to the compression force is around 1000N, so the pressure of the fluid introduced into the backpressure chamber of the back surface of the movable scroll may be low. Therefore, even if using a seal material for holding the pressure in the backpressure chamber, the load acting on the seal member will not become that large. Further, since the contact load is small, the lubrication state of the sliding surface of the seal member is believed to be in the fluid lubrication region, so an oil film is reliably formed on the surface of the housing side in sliding contact with the seal member and sliding contact is believed to be performed with a low coefficient of friction. Therefore, the mechanical loss due to the sliding action of the seal member can be kept low.
In a refrigeration cycle using as a refrigerant a so-called supercritical pressure fluid such as carbon dioxide (CO2), however, when compressing the refrigerant by a scroll compressor shown in the above related art, the thrust load acting on the movable scroll reaches as much as 7000N or about seven times the case of use of a refrigerant having a low working pressure such as a chlorofluorocarbon, so the pressure of the fluid introduced into the backpressure chamber similarly becomes a seven times higher pressure. This high-pressure acts on the seal member. Further, since the load acting on the seal member is high, the lubrication state of the sliding surface of the seal member is not in the fluid lubrication region, but is believed to be in the mixed lubrication region or boundary lubrication region where the coefficient of friction is high. Therefore, there is the problem that the mechanical loss due to the sliding action of the seal member becomes larger and causes a reduction in the efficiency of the compressor.
Therefore, in the related art later proposed by the inventors and disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2000-249086, there is described a scroll compressor using a supercritical pressure fluid as the refrigerant providing a seal member in a backpressure chamber of a movable scroll and taking out relatively low pressure refrigerant not yet compressed to a sufficiently high-pressure in the working chambers and supplying it to the backpressure chamber through a check valve so as to prevent in advance leakage of a large amount of high-pressure refrigerant from the backpressure chamber and so as to suppress an increase in the wear of the seal member or mechanical loss.
In this way, while the provision of a backpressure chamber behind an end plate of a movable scroll in order to support the thrust load in a scroll compressor and the provision of a seal member in the backpressure chamber in order to prevent leakage of the compressed fluid from the backpressure chamber are known even in a scroll compressor compressing a supercritical pressure fluid, details such as how to provide what kind of shape of seal member in the backpressure chamber have not yet been sufficiently researched.
Later research by the inventors proposing the above related art revealed that use of a seal member for the backpressure chamber having a joint such as in a piston ring of an internal combustion engine resulted in the problem of a large amount of high-pressure fluid supplied to the backpressure chamber leaking from the joint and that use of a continuous ring-shaped seal member not having any joint resulted in the problem of the compressed fluid entering the clearance between the seal member and wall surface of the backpressure chamber and therefore deformation of the seal member and obstruction of the action of closely contacting the wall surface of the backpressure chamber or the wall surface of the housing and a consequent inability to obtain a sufficient sealing effect.